fix: move check in AcctDiff::decode and use filtered len in AcctDiff::encode

[Fraser999]

Summary

Fixes two bugs in the BundleStateIndex journal codec (src/journal/coder.rs), both affecting AcctDiff round-tripping, and adds thorough boundary-case test coverage for every decode path. Bumps the patch version to 0.34.4.

Changes

• AcctDiff::decode length check (fb86156): the check_len! for the minimum diff size was run after the InfoOutcome had already been consumed, so it demanded a second outcome's worth of trailing bytes. Any minimum-size diff - notably an empty-storage account near the end of a buffer - was wrongly rejected with an Overrun. The check now runs up front, before decoding the outcome.
• AcctDiff::encode slot count (69e3e4e): encode wrote storage_diff.len() (the full map size) as the slot-count prefix but only serialized is_changed() entries. An unchanged slot made the on-wire count exceed the entries actually written, so decoding read a phantom slot - a clean overrun for a standalone diff, but silent corruption of the trailing new_contracts section inside a BundleStateIndex. encode now writes the count of changed slots, matching the write-loop and serialized_size.
• Test coverage: added boundary tests covering truncation (every strict prefix of a valid encoding must overrun), the exact AcctDiff minimum-size boundary, invalid tags for every tagged type, the unchanged-storage error, EIP-7702 / empty bytecode, empty index, and Option/Header round-trips. Both bug fixes have dedicated regression tests verified to fail before the fix and pass after.

API Breakages

None. No public signatures changed. Both fixes are confined to existing trait-method bodies. The decode fix only widens what is accepted (previously-rejected valid minimum diffs now decode), and the encode fix only changes bytes for directly-constructed diffs that violate the "no unchanged slots" invariant - output for data produced via the normal From<&BundleAccount> path is byte-identical.

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[Fraser999]

• fix: move check in AcctDiff::decode and use filtered len in AcctDiff::encode #160 👈 (View in Graphite)
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